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Don’t overreact to low pH levels in the fall

Chicken Little thought the sky was falling. It wasn’t. If you or a consultant pulled soil samples last fall before it rained and pH levels were low, let common sense prevail.

Think through possible causes and strategies before making rash decisions. Applying 300 pounds of pel lime ahead of soybeans just because pH dropped after a fall test could be a rash decision.

“We are big proponents of liming because of its impact on soil structure and soil life,” says Greg Kneubuhler, certified crop adviser, G & K Concepts, Harlan. However, pel lime may not be the answer, he says.

Key Points

Realize that low pH readings from early fall samples could be due to dry weather.

Compare pel lime versus ag lime on neutralizing power.

Decide if you have an emergency situation or a need for long-term investment.

“If we truly need calcium, pel lime may not offer the amount we need economically,” he continues. “Although an excellent source of calcium, 300 pounds of pel lime per acre only offers 108 pounds of soluble calcium.

“One ton of high-calcium ag lime can have 500 pounds of soluble calcium. So for the money, 1 ton of lime will go much farther than 300 pounds of pel lime. The pel lime could be a short-term Band-Aid if necessary in order to get lime applied.”

Low readings

How do you know if you need a Band-Aid? That’s where the effect of dry weather on pH test results becomes an issue. “Soil pH levels can test lower after droughty conditions because fertilizer salts remain in the soil, affecting lab readings,” says Jesse Grogan, CCA, LG Seeds, Lafayette.

Work at the University of Kentucky, uncovered by Betsy Bower, CCA, Ceres Solutions, Terre Haute, indicates that once rains return, as they did in late November, the salts wash out fairly quickly, allowing the pH reading to return to a more accurate level.

The key is if there are previous tests to compare against, Kneubuhler says. That’s why they test soils on a regular basis for most clients. Without a history of samples, it’s much more difficult to know if last fall’s low reading was a fluke due to conditions, or if the pH is low.

Dollars and cents

Whether or not to apply pel lime comes down to an economic decision for Darrell Shemwell, CCA, Posey County Co-op, Poseyville. The kicker is how low the pH truly is, he notes. In parts of southwestern Indiana, especially on red clay hillsides, pH can be low enough to affect crop growth.

If your pH is truly low, it would be highly likely that you would see a profitable response to pel lime, Shemwell says. At current grain prices a 2-bushel-per-acre yield increase would break even compared to the cost of the pel lime.

Grogan advises against falling for claims that pel lime can be applied at much lower rates than ag lime. Instead, he recommends comparing the value of pel lime vs. ag lime on a pound-per-pound basis as to neutralizing capability. He believes the best payoff for investment over time would be ag lime.

This article published in the April, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.